Latvia Prime Minister Valdis Dombrovskis resigned Wednesday after saying he is politically responsible for the collapse of a supermarket roof last week killed 54 people and wounded at least 40 others, the Associated Press reports.

Police are investigating the cause of the collapse, which was not weather-related. Investigators are looking into the possibility that substandard construction materials were used, or that the construction of a children’s playground on top of the supermarket may have contributed to the disaster, according to BBC. Police are also investigating whether government corruption may have played a roll.

The president of Latvia has described the disaster as “murder.”

Dombrovskis has been in office since 2009, and is the longest serving Latvian prime minister to date.